In installations comprisng a motor unit, a step-up or step-down gear unit, and a driven unit, the gears may be rapidly destroyed due to torsion vibrations in the shafts of the drive train. This destruction is linked to loss of contact between the teeth of two intermeshing gear wheels. Such loss of contact may be caused by oscillatory movements of the components of the drive train. Loss of contact gives rise to noise and to rapid destruction of the teeth by continuous hammering when operating at certain dangerous speeds. To avoid loss of contact, it is necessary for the amplitude A of the oscillating torque to be less than the average drive torque C.sub.0 (equal to the average delivered torque).
To avoid such loss of contact when the absolute value A of the oscillating torque amplitude is greater than the average drive torque C.sub.0, proposals have been made to pre-stress the teeth by means of an internal torque C.sub.1 which is added to the drive torque C.sub.0, but within the gear means only. This is done by means of a backlash takeup gear wheel. Such a gear wheel includes a main wheel and a secondary wheel, both of which mesh with a drive gear wheel, but with only the main gear wheel being keyed to the output shaft, and with the main wheel and the secondary wheel being urged to rotate relative to each other by at least one spring. This arrangement can naturally be applied to the driving gear wheel rather than to the driven gear wheel, with both solutions being equivalent.
Unfortunately, such as arrangement is in many cases insufficient. Preferred embodiments of the present invention provide a transmission system capable of preventing loss of contact between meshed gear wheels in substantially all circumstances which are encountered in practice.